move common test requirements to test/requirements.txt to simplify running tests outside of tox

Author: mattsb42-aws

test/requirements.txt

@@ -0,0 +1,4 @@
+mock
+pytest>=3.3.1
+pytest-cov
+pytest-mock

tox.ini

@@ -27,11 +27,7 @@ passenv =
     # Pass through AWS profile name (useful for local testing)
     AWS_PROFILE
 sitepackages = False
-deps =
-    mock
-    pytest>=3.3.1
-    pytest-cov
-    pytest-mock
+deps = -rtest/requirements.txt
 commands =
     local: pytest --cov aws_encryption_sdk -m local -l {posargs}
     integ: pytest --cov aws_encryption_sdk -m integ -l {posargs}